Rotary fluid machines are used in a wide variety of applications to transfer energy between fluid passing through the machine and a rotating mechanical assembly. In general, a rotary fluid machine has a housing with a fluid duct extending through the housing and one or more rotor assemblies which rotate within the fluid duct. In operation, the rotation of the rotor assemblies cause a difference in fluid pressure between the inlet and outlet of the fluid duct.
Rotary fluid machines are generally of either a beam-type configuration or of an overhung-type arrangement. U.S. Pat. No. 3,558,238 shows a typical rotary fluid machine of the overhung-type configuration. U.S. Pat. No. 3,758,226 shows a typical rotary fluid machine of the beam-type configuration.
In a typical beam-type machine, a shaft which forms part of the rotating assembly extends beyond both ends of the housing. Radial bearing assemblies are provided at each end of the housing to support the shaft in the housing while allowing the shaft to freely rotate about a rotational axis which extends along the length of the shaft and is generally parallel to the center of the shaft. A shaft seal assembly is located in either and of the housing at the point where the shaft passes through the housing. The shaft seal assembly restricts the passage of fluid between the inside and outside of the housing at the point where the shaft passes through the housing. Attached to and rotatable with the shaft are one or more impellers through which fluid passes. Rotary fluid machines of a beam-type configuration often have several impellers on the shaft. Several impellers are commonly used when a large difference between inlet fluid pressure and discharge fluid pressure exists. Typical impellers are designed such that fluid enters the impeller through an annular passage generally at the inner diameter of the impeller which is coaxial with the axis of rotation of the shaft. To provide a means for moving fluid in and out of the housing, inlet and discharge fluid passages are formed in the housing. Often these passages formed in the housing are positioned such that fluid entering the machine through the passage enters the fluid duct perpendicular to the axis of rotation of the shaft. After entering the fluid duct, the fluid must be aligned with the annular passage at the inlet of the impeller. The redirection of the fluid causes turbulence within the fluid stream which results in a pressure drop and a corresponding loss in machine efficiency.
A rotary fluid machine of the overhung configuration has a shaft forming part of the rotating assembly which extends beyond one end of the housing. Radial bearing assemblies are located in the end of the housing which the shaft passes through. The radial bearing assemblies support the shaft in the housing while allowing the shaft to freely rotate about the axis of rotation. The shaft is, therefore, supported in cantilever fashion. Attached to the section of shaft within the fluid duct are one or more impellers of similar design to the impellers of a beam-type machine. The impellers are typically of relatively large size and weight. When an impeller is mounted on the shaft being supported in cantilever fashion, high radial forces must be resisted by the bearing assemblies. Large bearing forces require large capacity radial bearings which are often undesirable. The problem of large radial bearing forces can be especially acute when more than one impeller is placed on the shaft to form a multistage rotary fluid machine. Overhung rotary fluid machines are therefore often limited to one or two impellers.
A fluid passage can be formed in the end of the housing the shaft does not extend through, such that fluid moving through the passage enters the machine parallel to and coaxial with the axis of rotation of the shaft, and therefore, does not have to be redirected into the impellers. The turbulence and associated loss of machine efficiency due to the redirection of the fluid is substantially avoided.
It is, therefore, apparent that a rotary fluid machine with a fluid passage coaxial with the shaft axis of rotation, and with the impellers located between the radial bearing assemblies, would be a useful addition to the art.